Add a rate tracker that tracks rate over a given interval split up into buckets that accumulate uni…

webrtc/base/bucketratetracker.cc

Index: webrtc/base/bucketratetracker.cc
diff --git a/webrtc/base/bucketratetracker.cc b/webrtc/base/bucketratetracker.cc
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+/*
+ *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/base/bucketratetracker.h"
+
+#include <stddef.h>
+#include <assert.h>
+
+#include <algorithm>
+
+#include "webrtc/base/timeutils.h"
+
+namespace rtc {
+
+BucketRateTracker::BucketRateTracker(
+    uint32 bucket_milliseconds, size_t bucket_count)
+    : bucket_milliseconds_(bucket_milliseconds),
+    bucket_count_(bucket_count),
+    sample_buckets_(new size_t[bucket_count + 1]),
+    bucket_start_time_(~0u) {
+  assert(bucket_milliseconds > 0u);
+  assert(bucket_count > 0u);
+}
+
+BucketRateTracker::~BucketRateTracker() {
+  delete[] sample_buckets_;
+}
+
+double BucketRateTracker::ComputeCurrentRate(
+    uint32 interval_milliseconds) const {
+  if (bucket_start_time_ == ~0u) {
+    return 0.0;
+  }
+  uint32 current_time = Time();
+  // Calculate which buckets to sum up given the current time.  If the time
+  // has passed to a new bucket then we have to skip some of the oldest buckets.
+  uint32 available_interval_milliseconds = std::min<uint32>(
+      interval_milliseconds,
+      bucket_milliseconds_ * static_cast<uint32>(bucket_count_));
+  // number of old buckets (i.e. after the current bucket in the ring buffer)
+  // that are expired given our current time interval.
+  size_t buckets_to_skip;
+  // Number of milliseconds of the first bucket that are not a portion of the
+  // current interval.
+  uint32 milliseconds_to_skip;
+  if (current_time > initialization_time_ + available_interval_milliseconds) {
+    uint32 time_to_skip = current_time - bucket_start_time_ +
+        static_cast<uint32>(bucket_count_) * bucket_milliseconds_ -
+        available_interval_milliseconds;
+    buckets_to_skip = time_to_skip / bucket_milliseconds_;
+    milliseconds_to_skip = time_to_skip % bucket_milliseconds_;
+  } else {
+    buckets_to_skip = bucket_count_ - current_bucket_;
+    milliseconds_to_skip = 0u;
+    available_interval_milliseconds = current_time - initialization_time_;
+  }
+  // If we're skipping all buckets that means that there have been no samples
+  // within the sampling interval so report 0.
+  if (buckets_to_skip > bucket_count_ ||
+      available_interval_milliseconds == 0u) {
+    return 0.0;
+  }
+  size_t start_bucket = NextBucketIndex(current_bucket_ + buckets_to_skip);
+  // Only count a portion of the first bucket according to how much of the
+  // first bucket is within the current interval.
+  size_t total_samples = sample_buckets_[start_bucket] *
+      (bucket_milliseconds_ - milliseconds_to_skip) /
+      bucket_milliseconds_;
+  // All other buckets in the interval are counted in their entirety.
+  for (size_t i = NextBucketIndex(start_bucket);
+      i != NextBucketIndex(current_bucket_);
+      i = NextBucketIndex(i)) {
+    total_samples += sample_buckets_[i];
+  }
+  // Convert to samples per second.
+  return static_cast<double>(total_samples * 1000u) /
+      static_cast<double>(available_interval_milliseconds);
+}
+
+void BucketRateTracker::AddSamples(size_t sample_count) {
+  EnsureInitialized();
+  uint32 current_time = Time();
+  // Advance the current bucket as needed for the current time, and reset
+  // bucket counts as we advance.
+  for (size_t i = 0u; i <= bucket_count_ &&
+      current_time >= bucket_start_time_ + bucket_milliseconds_; ++i) {
+    bucket_start_time_ += bucket_milliseconds_;
+    current_bucket_ = NextBucketIndex(current_bucket_);
+    sample_buckets_[current_bucket_] = 0u;
+  }
+  // Ensure that bucket_start_time_ is updated appropriately if we've expired
+  // the entire buffer of samples.
+  bucket_start_time_ += bucket_milliseconds_ *
+      ((current_time - bucket_start_time_) / bucket_milliseconds_);
+  // Add all samples in the bucket that includes the current time.
+  sample_buckets_[current_bucket_] += sample_count;
+}
+
+uint32 BucketRateTracker::Time() const {
+  return rtc::Time();
+}
+
+void BucketRateTracker::EnsureInitialized() {
+  if (bucket_start_time_ == ~0u) {
+    initialization_time_ = Time();
+    bucket_start_time_ = initialization_time_;
+    current_bucket_ = 0u;
+    // We only need to initialize the first bucket because we reset buckets when
+    // current_bucket_ increments.
+    sample_buckets_[current_bucket_] = 0u;
+  }
+}
+
+size_t BucketRateTracker::NextBucketIndex(size_t bucket_index) const {
+  return (bucket_index + 1u) % (bucket_count_ + 1u);
+}
+
+}  // namespace rtc